export class Frontend {
  contentTypes = {
    html: 'text/html; charset=utf-8',
    js: 'text/javascript',
    css: 'text/css',
    md: 'text/plain',
    txt: 'text/plain',
    png: 'image/png',
    jpg: 'image/jpg',
    webm: 'image/webm',
    svg: 'image/svg',
  }

  constructor({apiBaseUrl, appBaseUrl}) {
    this.apiBaseUrl = apiBaseUrl
    this.appBaseUrl = appBaseUrl
    this.files = {}
  }

  repoUrl(user, repo) {
    return (
      this.apiBaseUrl +
      '/repos' +
      '/' + encodeURIComponent(user) +
      '/' + encodeURIComponent(repo)
    )
  }

  pathString(path) {
    return path.map(s => (
      '/' + encodeURIComponent(s)
    )).join('')
  }

  rawUrl(user, repo, commit, path) {
    return (
      this.appBaseUrl +
      '/' + encodeURIComponent(user) +
      '/' + encodeURIComponent(repo) +
      '/raw/commit' +
      '/' + encodeURIComponent(commit) +
      this.pathString(path)
    )
  }

  checkOk(resp) {
    if (!resp.ok) {
      throw new Error('not ok - ' + JSON.stringify(
        {status: resp.status, url: resp.url}
      ))
    }
  }

  async loadFile(user, repo, commit, src, dest) {
    const url = this.rawUrl(user, repo, commit, src)
    const resp = await fetch(url)
    this.checkOk(resp)
    const body = await resp.arrayBuffer()
    const ext = dest.at('-1')?.match?.(/\.(\w+)$/)?.[1]
    const contentType = this.contentTypes[ext]
    this.files[this.pathString(dest)] = {
      user,
      repo,
      commit,
      body,
      contentType: contentType ?? 'application/octet-stream',
    }
  }

  contentsUrl(user, repo, path, ref) {
    const url = new URL(
      this.repoUrl(user, repo) +
      '/contents' +
      this.pathString(path)
    )
    if (ref !== undefined) {
      const search = new URLSearchParams()
      search.set('ref', ref)
      url.search = search.toString()
    }
    return url.toString()
  }

  async loadRepo(user, repo, opts) {
    const {
      srcPath = [], destPath = [], ref
    } = opts
    const url = this.contentsUrl(
      user, repo, srcPath, ref
    )
    const resp = await fetch(url)
    this.checkOk(resp)
    const contents = await resp.json()
    await Promise.all(contents.map(item => (
      item.type === 'dir' ?
      this.loadRepo(user, repo, {
        ...opts,
        srcPath: [...srcPath, item.name],
        destPath: [...destPath, item.name],
      }) :
      this.loadFile(
        user,
        repo,
        item.last_commit_sha,
        [...srcPath, item.name],
        [...destPath, item.name],
      )
    )))
  }

  async serve(event) {
    const {pathname} = new URL(event.request.url)
    if (pathname in this.files) {
      const file = this.files[pathname]
      event.respondWith(new Response(file.body, {
        status: 200,
        headers: {
          'Content-Type': file.contentType,
        },
      }))
    } else {
      event.respondWith(new Response(
        'Not Found', {status: 404}
      ))
    }
  }
}